Messages in this thread |  | | Date | Tue, 17 Feb 2015 11:58:39 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 3/8] x86, fpu: kill save_init_fpu(), change math_error() to use unlazy_fpu() |
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On 02/16, Rik van Riel wrote: > > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 02/16/2015 04:09 PM, Borislav Petkov wrote: > > On Fri, Feb 06, 2015 at 03:02:00PM -0500, riel@redhat.com wrote: > >> From: Oleg Nesterov <oleg@redhat.com> > > >> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > >> index fb4cb6adf225..51c465846f06 100644 --- > >> a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -663,7 > >> +663,7 @@ static void math_error(struct pt_regs *regs, int > >> error_code, int trapnr) /* * Save the info for the exception > >> handler and clear the error. */ - save_init_fpu(task); + > >> unlazy_fpu(task); > > > > Do I see it correctly that even with this there's a not-so-small > > hole *after* conditional_sti() and *before* unlazy_fpu() where > > caller can still get preempted? > > That's ok, the context switch will save the register contents > to memory in that case.
Yes, thanks.
> At that point unlazy_fpu will potentially > do nothing, and the task will process the FPU context that was > saved to memory previously.
Or, if __thread_has_fpu() will be true again, it will save the registers again.
And this equally applies to any other user of unlazy_fpu().
Oleg.
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